Switching assembly for a hydraulic pump jack

ABSTRACT

A switching assembly for a hydraulic pump jack has a non-magnetic cylinder and a piston that is reciprocally movable within the interior bore of the cylinder. The piston has circumferential sealing means to engage the interior surface of the cylinder, and carries a magnetic element. A fluid source supplies a working fluid to the cylinder to move the piston within the cylinder. At least one magnetic sensor having a unique sensor value is externally mounted adjacent to the non-magnetic cylinder and senses at least a top of a piston stroke and the bottom of the piston stroke. A controller receives signals from the magnetically-actuated sensors as the magnetic element carried by the piston comes in proximity with and influences the at least one magnetic sensor. The controller controls piston positioning by selectively controlling the flow of working fluid to the cylinder.

FIELD

The present switching assembly is intended for use with a hydraulic pump jack to improve switching by more accurately determining piston position and speed.

BACKGROUND

Switching assemblies presently used for hydraulic pump jacks consist of two axially-spaced ports equipped with fittings in which are positioned electric-over-hydraulic switches. The positioning of these ports determines the upper limit and the lower limit of the piston stroke. The electric-over-hydraulic switches are tied into an electrically-controlled hydraulic spool valve. Variations in hydraulic pressure at the ports results in the switches causing the hydraulic spool valve to reverse the direction and flow of hydraulic working fluid.

SUMMARY

The present disclosure teaches a switching assembly for a hydraulic pump jack, comprising a non-magnetic cylinder with an exterior surface and an interior surface that defines an interior bore. A piston is reciprocally movable within the interior bore of the cylinder, with the piston having circumferential sealing means to engage the interior surface of the cylinder. A magnetic element is carried by the piston. A fluid source supplies a working fluid to the cylinder, wherein the piston is moved by injecting working fluid into the cylinder. At least one magnetic sensor, or an array of axially-spaced, magnetically-triggered sensors, is externally mounted adjacent to the non-magnetic cylinder for sensing at least a top of a piston stroke and the bottom of the piston stroke. A controller receives signals from the magnetically-actuated sensor as the magnetic element carried by the piston comes in proximity with and influences the magnetic sensor or sensors. The controller controls piston positioning by selectively controlling the working fluid supplied by the fluid source to the cylinder.

In preferred embodiments, each of the magnetically-triggered sensors has a unique sensor value. The unique sensor values allow the controller to determine the precise axial position of the piston inside the cylinder, based upon the unique sensor value of the signals received by the controller. The unique sensor values of the magnetically-triggered sensors in an array of such sensors preferably vary incrementally. The unique sensor value of at least one sensor in the array may be a resistance value.

According to another aspect, the cylinder may have a lower end and an upper end, with the upper end being higher than the lower end. The working fluid serves to raise the piston from the lower end toward the upper end of the cylinder, and gravity serves to return the piston from the upper end to the lower end of the cylinder.

According to another aspect, the magnetic sensor may be a linear displacement transducer sensor bar that extends along the height of the non-magnetic cylinder.

According to another aspect, the switching assembly may further comprise a seal for sealing the well when the piston is in a lower position, the non-magnetic cylinder being removable to expose the piston in the lower position.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features will become more apparent from the following description in which reference is made to the appended drawings, which are for the purpose of illustration only and are not intended to be in any way limiting, and wherein:

FIG. 1 is a perspective view of a switching assembly for a hydraulic pump jack.

FIG. 2 is a side elevation of the hydraulic pump jack from the switching assembly of FIG. 1.

FIG. 3 is a side elevation, in section, of the hydraulic pump jack from the switching assembly of FIG. 1.

FIG. 4 is a side elevation view of a piston in one embodiment of the hydraulic pump jack.

FIG. 5 is a detailed side elevation view, in section, of the piston in a lower, locked position.

FIG. 6 is a circuit board schematic for a switching assembly.

DETAILED DESCRIPTION

A switching assembly for a hydraulic pump jack generally identified by reference numeral 10, will now be described with reference to FIGS. 1-6.

Structure and Relationship of Parts:

Referring to FIG. 1, a switching assembly for a hydraulic pump jack 10 includes a non-magnetic cylinder 12 in combination with a control unit 18 that includes an electronic controller and a hydraulic fluid source (concealed within control unit 18). Referring to FIG. 3, positioned within non-magnetic cylinder 12 is a piston 14. Referring to FIG. 4, a magnetic element 16 is mounted on piston 14. Referring to FIG. 3, an externally-mounted, magnetically-triggered sensor 20 that extends along the length of non-magnetic cylinder 12 is responsive to the position of piston 14. Referring to FIG. 5, this is due to the proximity to magnetic element 16, which is carried by piston 14.

In one example, sensor 20 is a linear displacement transducer (“LDT”) that employs magnetostrictive technology. A magnetostrictive LDT works roughly as follows. An interrogation pulse is transmitted along a waveguide in the sensor bar. When the magnetic field generated by the pulse interacts with the magnetic field of a permanent magnet that is positioned somewhere along the waveguide, a strain pulse is generated and returned back toward the transmitter. The time elapsed between the transmitting the interrogation pulse and the receiving of the strain pulse is proportional to the distance between the transmitter and the permanent magnet. A processor then converts the elapsed time into an electrical signal that represents the distance between the transmitter and the permanent magnet.

In the present example, the LDT sensor 20 is mounted on the outside of the lifting cylinder 12, and the permanent magnet 16 is located inside the cylinder 12 and travels up and down with the polish rod, such as on piston 14 as shown. As the permanent magnet 16 travels up and down, sensor bar 20 measures the distance between the transmitter and the magnet, which relates to the position of piston 14, with an accuracy that may approach +/−0.1 inches. The electrical output signal representing the position of the polish rod may be updated at much as 300 times per second or more. It will be recognized by those of ordinary skill in the art that other magnetically-actuated switches may also be used that determine the position of piston 14, and sensor 20 may include multiple sensing elements, or multiple types of sensors. If discrete sensors are used, at least two are required: one for the top, and another for the bottom.

Referring to FIG. 1, control unit 18 receives signals from the magnetically-triggered sensor or sensors 20 and is able to determine the position of piston 14.

Referring to FIG. 2, the non-magnetic cylinder 12 has an exterior surface 24, a lower end 30 and an upper end 32 that is higher than the lower end 30. Referring to FIG. 3, the non-magnetic cylinder includes an interior surface 26 that defines an interior bore 28. Piston 14 is reciprocally movable within the interior bore 28 of the cylinder 12.

Referring to FIG. 5, piston 14 has circumferential seals 34 to engage the interior surface 26 of the cylinder 12. Referring to FIG. 1, the hydraulic fluid source within control unit 18 supplies a hydraulic working fluid to the cylinder 12.

Referring to FIG. 3, the hydraulic working fluid causes the piston 14 to be raised from the lower end 30 of the cylinder 12 toward the upper end 32 of the cylinder 12 by an injection of working fluid 36 into the cylinder 12. The piston 14 returns from the upper end 32 to the lower end 30 by force of gravity.

Referring to FIG. 3, the sensor or sensors 20 are carried by a sensor bar mounted to the exterior surface 24 of the cylinder 12 at axially-spaced and preferably regular intervals. As shown, the sensor bar spans the full length of the non-magnetic stainless steel cylinder 12, and an electronic instrument is wired to this sensor bar and reads the signal generated by the magnet in a particular location.

Each of the magnetically-triggered sensors 20 has a unique sensor value or resistance value. In a preferred embodiment, the unique sensor values of the magnetically-triggered sensors 20 in the array vary incrementally from the lower end 30 of the cylinder 12 to the upper end 32 of the cylinder 12. In the illustrated exemplary embodiment, the sensor bar houses 10 six-inch-long circuit boards. Each circuit board holds two electronic reed switches and a 100-ohm resistor (for a total of 20 reed switches). The circuit boards are stacked end-to-end, with the “signal out” of one circuit board being connected to the “signal out” of the next circuit board. Therefore, the resistance of any switch will be equal to 100+n*100, where n is the switch number. For example, the resistance of switch #1 will be 200 ohms, the resistance of switch #5 will be 600 ohms, and the resistance of switch #20 will be 2100 ohms. The sensor bar spans the full length of the non-magnetic stainless steel cylinder 12. An electronic instrument is wired to this sensor bar and reads the resultant resistance changes as the magnetic element 16 carried by the piston 14 passes by each reed switch and closes it. The electronic controller in control unit 18 reads the switch-input line 120 times per second. The controller looks for the first time a given switch closes, then waits 25 milliseconds and reads the unique sensor value (typically a resistance value) to determine which switches is closed. FIG. 6 illustrates a circuit board layout for the magnetically-triggered sensors.

Referring to FIG. 3, the magnetically-triggered sensor or sensors 20 is or are excited as the magnetic element 16 carried by the piston 14 comes in proximity with and influences the sensors, or, in one embodiment, as it influences the magnetic field within the LDT bar. This enables the electronic controller within control unit 18 to determine precise piston positioning based upon the unique sensor value of the signals received and control movement of piston 14 by selectively controlling the working fluid supplied to the cylinder 12. Within 8 inches of movement, the electronic controller knows the axial position of the piston 14 in its travel within the cylinder 12, and because it now has a time-and-distance equation between two switches closures, it now can adjust the supply of hydraulic fluid to speed up or slow down to a selected number of strokes per minute programmed into the controller. The stroke length can be programmed to start and stop anywhere between three switch points along the length of cylinder 12.

In one embodiment, the LDT bar allows the electronic controller to know where the piston is in its travel within 0.1 inches of movement such that it can adjust the supply of hydraulic fluid to speed up or slow down to the programmed strokes per minute. When sensor 20 is an LDT bar, the stroke length can be programmed to start and stop at any desired location along the length of cylinder 12.

Operation:

In the description below, the embodiment that uses the LDT bar is described. Referring to FIG. 3, hydraulic working fluid supplied by the hydraulic fluid source within control unit 18, enters the cylinder 12 causing the piston 14 to rise towards the upper end 32 of the cylinder 12, away from the lower end 30. As the piston 14 moves upwards, the magnetic element 16 (best shown in FIG. 4) interacts with the sensors 20 on the sensor bar, exciting the circuit illustrated in FIG. 6. Signals from the sensor bar are sent to an electronic controller within control unit 18. The electronic controller determines precise piston positioning and controls movement by selectively controlling the working fluid supplied to the cylinder 12. At the termination of each stroke, the force of gravity is used to move the piston 14 downwards towards lower end 30 and away from upper end 32.

Advantages:

To increase or decrease the speed of the cylinder with prior art devices is a complicated process of adjusting the flow of the pump and timing the strokes by watching a pressure gauge. When the pressure goes high, the time clock is activated, and when the pressure goes low it is stopped. The time elapsed is then used to calculate the speed of the cylinder. This can be a time-consuming process of adjusting and waiting for the desired results.

The systems used previously have many undesirable features. First and foremost is the potential of the hydraulic cylinder to leak at any of the locations along its length where the ports are located. The electric-over-hydraulic switches are prone to failure, and their life span is very limited due to the fact that they are mechanical switches. The operator also has to uncouple and recouple these switches manually and put them into the positions required for the desired stroke length. There is also a danger of spilled hydraulic fluid any time this is done.

Systems in accordance with the present disclosure do not require pressure ports through which fluids could leak. These systems are intrinsically safe, as they do not require high enough voltage or amperage to produce a spark, thus eliminating or greatly reducing the risk wellhead explosions. Nonetheless, they preferably have explosion-proof classification in Class 1, Division 2 areas around the wellhead, for even greater protection against the risk of wellhead explosions. Systems in accordance with the present disclosure enable the operator of a hydraulic pump jack to know the position and speed of the hydraulic cylinder within 8 inches of stroke travel.

In addition, as the system is completely sealed, piston 14 may be more easily serviced. Referring to FIG. 5, piston 14 is lowered to the lower end 30 of piston cylinder 12 and locked into place using a common wellhead lock or safety valve, such as a blowout preventer 38. As shown, once locked down, the wellbore is sealed, such that cylinder 12 may be removed to allow access to piston 14 without the use of a service rig to hold the weight of the rod string. At this point, piston 14 may be serviced or replaced while keeping the well shut in and allows the full weight of the string to be held independently of any lifting equipment, while maintaining full containment on the well. The piston design allows the cylinder to be removed without disconnecting the sucker rod or the polish rod and exposing the wellhead to the atmosphere. This function allows cost savings and easy servicing.

Most of the hydraulic cylinders presently manufactured use a steel outer tube with a steel piston rod and a steel piston. In magnetics, it is known that steel acts as a shunt, where the magnetic lines of flux will not pass through steel. The present system is manufactured using non-magnetic materials. For example, in one embodiment, the outer cylinder tube is manufactured using non-magnetic stainless steel, the piston is manufactured using non-magnetic aluminum, and the piston rod is manufactured using high-quality steel. The aluminum piston houses a magnet which may be a rare earth neodymium iron boron magnet with high-strength magnetic characteristics.

The presently-described system enables the operator to know the position and the speed of the hydraulic piston within a fraction of an inch, if desired. The preferred embodiment uses an LDT sensor bar that spans the full length of a non-magnetic stainless steel cylinder and enables the user to adjust the hydraulics to speed up or slow down to the programmed strokes per minute. The stroke length can be programmed to start and stop anywhere between various switch points along the length of the hydraulic cylinder to an accuracy of up to 0.1 inches in some embodiments.

Traditional electric-over-hydraulic switches used on most hydraulic pump jacks utilize a diaphragm which, when hydraulic pressure pushes against it, either opens or closes a mechanical toggle switch. Because of the mechanical nature of this design, there is a limit to the number of times it can be activated. A high-quality mechanical switch typically has a life expectancy of about 2 million cycles. In contrast, the electronic reed switch used in embodiments in accordance with the present disclosure typically has a life expectancy of 20 million cycles. This is ten time times the life expectancy of a traditional electric-over-hydraulic switch, making the life expectancy of the presently-disclosed systems much greater than that of traditional hydraulic strokers.

The first circuit board's “signal in” terminal is connected to the amphanol plu pins A and B at the base of the sensor bar. The sensor bar is then installed to the cylinder 12 using four stainless steel corban gear clamps. This type of mounting allows for the sensor bar to be rapidly mounted and dismounted, thus greatly enhancing field serviceability.

In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one such element.

The following claims are to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, and what can be obviously substituted. Those skilled in the art will appreciate that various adaptations and modifications of the described embodiments can be configured without departing from the scope of the claims. The illustrated embodiments have been set forth only as examples and should not be taken as limiting the scope of the disclosure or the claims. It is to be understood that, within the scope of the following claims, embodiments in accordance with the present disclosure may be practiced other than as specifically illustrated and described. Any use of any form of the word “typical” is to be interpreted in the sense of being representative of common usage or practice, and not as implying essentiality or invariability. 

What is claimed is:
 1. A switching assembly for a hydraulic pump jack, said switching assembly comprising: (a) a non-magnetic cylinder having an exterior surface and an interior surface, said interior surface defining an interior bore; (b) a piston reciprocally movable within the interior bore of the cylinder and having circumferential sealing means engageable with the interior surface of the cylinder; (c) a magnetic element carried by the piston; (d) an array of magnetically-triggered sensors mounted to the exterior surface of the cylinder at selected axially-spaced intervals; and (e) a controller adapted to receive signals from the magnetically-triggered sensors; wherein: (f) the cylinder is adapted to receive a working fluid such that the piston is axially movable within the cylinder in response to injection of working fluid into the cylinder; (g) the controller will receive signals from the magnetically-triggered sensors as the magnetic element carried by the piston comes in proximity with and influences the magnetically-triggered sensors as the piston moves axially within the cylinder; and (h) the controller is adapted to control the axial position of the piston within the cylinder by selectively controlling the flow of working to the cylinder.
 2. The switching assembly of claim 1, wherein: (a) the cylinder has a lower end and an upper end; (b) the cylinder is adapted to receive a working fluid proximal to said lower end of the cylinder, such that injection of a working fluid into the cylinder will cause upward movement of the piston within the cylinder; and (c) gravity will effect downward movement of the piston within the cylinder.
 3. The switching assembly of claim 1, wherein: (a) each of the magnetically-triggered sensors has a unique sensor value; and (b) the controller is adapted to determine the axial position of the piston within the cylinder based upon the unique sensor values of the signals received from the magnetically-triggered sensors.
 4. The switching assembly of claim 3, wherein the unique sensor value of each of the magnetically-triggered sensors in the array varies incrementally.
 5. The switching assembly of claim 3, wherein the unique sensor value associated with at least one of the magnetically-triggered sensors is a resistance value.
 6. A switching assembly for a hydraulic pump jack, said switching assembly comprising: (a) a non-magnetic cylinder having: a.1 an exterior surface and an interior surface, said interior surface defining an interior bore; a.2 a lower end; and a.3 an upper end that is higher than the lower end; (b) a piston reciprocally movable within the interior bore of the cylinder, the piston having circumferential sealing means to engage the interior surface of the cylinder; (c) a magnetic element carried by the piston; (d) a fluid source supplying a hydraulic working fluid to the cylinder, such that injection of working fluid into the cylinder will cause the piston to move toward the upper end of the cylinder; (e) an array of magnetically-triggered sensors mounted to the exterior surface of the cylinder at selected axially-spaced intervals, each said magnetically-triggered sensor having a unique sensor value, wherein the unique sensor value of each magnetically-triggered varies incrementally from the lower end of the cylinder to the upper end of the cylinder; and (f) a controller adapted to receive signals from the magnetically-triggered sensors; wherein: (g) the controller will receive signals from the magnetically-triggered sensors as the magnetic element carried by the piston comes in proximity with and influences the magnetically-triggered sensors as the piston moves axially within the cylinder; and (h) the controller is adapted to determine precise piston positioning within the cylinder based upon the unique sensor values of the signals received and controlling piston movement by selectively controlling the flow of working fluid from the fluid source to the cylinder.
 7. The switching assembly of claim 6, wherein the unique sensor value associated with at least one of the magnetically-triggered sensors is a resistance value.
 8. The switching assembly of claim 6, wherein downward movement of the piston within the cylinder is effected by gravity. 